Icons on workflow toolbox are blurred

I'm re-hosting the designer in my own application. But I surprisingly found the icons in the toolbox are blurred. Screenshot is upload here.

It seems the toolbox is stretched, but the text is displayed correctly, only the icons are blurred. The screenshot was taken from one WF sample (WF_WCF_Samples\WF\Basic\DesignerRehosting\Basic\cs). The only change I made was making the toolbox list开发者_运维技巧 long enough, and assigning the same icon (16x16) to all the tools. You can find the sample codes here.

Any idea what's going wrong? Is there any workaround available?

Thanks so much! Donald

Set UseLayoutRounding="True" on the Main Window. That fixes it.